In our NT passage we see that, as believers, our lives need to be different than the lives of the non-believers around us.
Robert Rayburn says....
Christians’ behavior, in other words, is to be different than even the best behavior of unbelievers because they have a very different reason for their behavior. Unbelievers can certainly do good things, but there is definitely a limit to what they will do and there is almost always a principle of self-interest at work. Christians have completely different motivations which lend a completely different character to their obedience. In fact, the ancient moralists almost always recommended the principle in this way: “Do good to others so they will do good to you.” Christians, on the other hand, are to seek to please a merciful God.... If we would be the true children of our heavenly Father we should have the same spirit toward our enemies as he does toward his and, of course, we were once his enemies....
The problem we face is that Christianity has been around for a long time now and only some of those who call themselves Christians take seriously the Lord’s summons to his disciples that they must live a life different from and higher than even that of the most moral of unbelievers. Our faith and the reputation of our religion have been profoundly compromised in the so-called Christian world. We are no longer and so obviously a .... unique people. But some of us must be. Some of us must keep alive that reputation in the world. Some of us must persuade the unbelieving world that there really is such a community as Jesus Christ has described here. There is very little that we can do about the fact that so many insincere Christians dilute our testimony in the world, but there is nothing this world needs more than that there should be a mass of Christian people who vindicate in their lives the description of true Christianity that our Savior has given here.
I don’t suppose a one of us really has any difficulty understanding what the Lord Jesus is teaching us here, no matter that nearly 2,000 years separates his time from our own. When a store clerk is rude, the Lord expects us to be patient and kind in return. When we are criticized, even when we are criticized in ways we think unjust, we are to respond humbly, ready to take any responsibility that is ours and to reply with courtesy and respect. When people make demands upon us that are really unfair, we ought to meet them cheerfully, even sacrificially. Our loving treatment of others is vastly more important than any injustice done to us. If, as is happening in Iran and elsewhere today, we are condemned to death for our faith in Christ, we are to love and pray for our enemies to the end as our Savior did, as Stephen did and as countless martyrs have done after them. In all things we ought to govern our conduct by the principle of mercy, and not just any principle of mercy. No, the mercy, the kindness, the generosity, the patience toward others that is to mark our behavior... is that mercy that our heavenly Father and our Savior showed us in saving us from our sins, in overlooking our disgusting faults, and in paying the terrible price he paid to remove our mountainous guilt when he knew full well he was going to get virtually nothing in return.
That is the kind of mercy to which we are to aspire in our conduct toward others.... We return blessing to those who curse us because we cursed God and he blessed us in return. We give to those who beg from us because we were nothing but beggars and the Lord lavished his gifts on us.
It isn’t only that we ought to behave this way toward others and toward our enemies, Christians want to do this; no, that isn’t even strong enough. They revel in doing it! Or, they should.
You see, this way of life, this radical, extravagantly selfless way of life, is the way of life a Christian wants to live precisely because of the impression the Lord’s love and mercy has made upon his or her soul. A person cannot really appreciate God’s great mercy, cannot feelingly understand what God’s grace has done in his or her life sinful and selfish life and not want that grace to be embodied in his or her behavior toward others. A Christian cannot really love God without wanting to please him. But how can mere mortals like you and me please God? We can take his heart and make it our own. We can honor his love – selfless, radical, sacrificial – by making it our own. We should; we must.... To do anything less is to belittle that love with which he loved us. If you don’t aspire to God’s kind of love then it must not have impressed you very much.